Today the energy requirements of the transport sectors are dominated by liquid fuels derived from the fractionation and processing of crude oil. The dominance of liquid fuels is expected to continue.
Crude oils derived from liquid fuels usually are not clean. They typically contain significant amounts of sulphur, nitrogen and aromatics. Diesel fuels derived from crude oil show relatively low cetane values. Clean distillate fuels can be produced from petroleum based distillates through (severe) hydrotreatment at great expense. For diesel fuels, however, these treatments usually hardly improve the cetane number.
Another source for distillate fuels, especially middle distillates, i.e. kerosene and diesel, is the Fischer-Tropsch process, especially using cobalt catalysts. During the last two decades this process has evolved as a key process for the conversion of natural gas into especially middle distillates of high quality. In this process synthesis gas is converted in several steps into middle distillates. First, natural gas in converted into synthesis gas by means of a (catalytic) partial oxidation process and/or steam reforming process. In a second step the synthesis gas is converted into long chain paraffins (the average C5+ hydrocarbon usually comprising 25 to 35 carbon atoms). In a third step the long chain hydrocarbons are hydrocracked into molecules of the desired middle distillate fuels. In this respect reference is made to EP 161 705, EP 583 836, EP 532 116, WO 99/01218, U.S. Pat. No. 4,857,559 and EP 1 004 746. Further reference is made to H M H van Wechem and M M G Senden, Conversion of Natural Gas to Transportation Fuels, Natural Gas Conversion II, H E Curry-Hyde and R F Howe (editors), Elsevier Science B.V. pages 43-71.
In general, the quality of the middle distillates prepared by the Fischer-Tropsch process is excellent. The mainly paraffinic products are free from sulphur, nitrogen and aromatic compounds. The kerosene and diesel have excellent combustion properties (smoke point and cetane number). The cold flow properties meet the relevant specifications. If necessary, additives may be used to meet the most stringent cold flow specifications. In addition, also the usual additives may be added.
In view of the continuously increasing requirements of the middle distillate properties, there is a need to further improve the middle distillate properties, especially the cold flow properties of the middle distillates. Thus, there is a need for middle distillates with improved intrinsic cold flow properties, i.e. these properties are to be obtained without using any further treatment of the fuels (e.g. dewaxing) or without the use of any additives. In addition, for the diesel fraction it is desired that T95, the temperature at which 95 vol % amount of diesel boiling, is 380° C. or less, preferably 370° C. or less, more preferably 360° C. or less, the density (15° C.) should be 840 kg/m3 or less, preferably 800 kg/m3 or less, more preferably 780 kg/m3 or less and the amount of (poly)aromatic compounds should be zero.